1. Field of the Invention
This invention relates to reflector antennas. More particularly, the invention relates to an improved subreflector beam steering arrangement operable to compensate for focus errors arising from thermal expansion and/or contraction of the reflector assembly and/or support apparatus.
2. Description of Related Art
Electrically large reflector antennas enable satellite to earth station RF communication links with extremely narrow beamwidths. Typically, the earth station reflector antenna is aligned with the orbital path of the target satellite via a tracking mount that orients the entire antenna assembly to align the reflector antenna with the satellite. Due to the significant weight and windloading inherent in a large reflector antenna, tracking mounts with precision alignment capability, for example ±0.05 degrees or less, significantly increase the cost and complexity of the resulting earth station.
Commonly owned U.S. Pat. No. 6,943,750, “Self-Pointing Antenna Scanning” by Brooker et al, issued Sep. 13, 2005, hereby incorporated by reference in its entirety, discloses an antenna alignment assembly for a reflector antenna utilizing orthogonal adjustments made to the position of the subreflector with respect to the main reflector. This subreflector tracking technology is particularly useful, for example, for small beam alignment adjustments between the reflector antenna and a satellite in geosynchronous orbit as the satellite wobbles and/or drifts within its orbit. Handling these small alignment adjustments via subreflector tracking technology significantly simplifies the requirements of an additional tracking mount, if any.
Competition in the reflector antenna market has focused attention on improving electrical performance and minimization of overall manufacturing, inventory, distribution, installation and maintenance costs. Therefore, it is an object of the invention to provide a reflector antenna and/or sub-system(s) that overcome deficiencies in the prior art.